JERUSALEM - With the purchase of two more German-made Dolphin submarines capable of carrying nuclear warheads, military experts say Israel is sending a clear message to Iran that it can strike back if attacked by nuclear weapons.

The purchases come at a time when Iran is refusing to bow to growing Western demands to halt its nuclear program, and after Iranian President Mahmoud Ahmadinejad has called for Israel to be "wiped off the map."

The new submarines, built at a cost of $1.3 billion with Germany footing one-third of the bill, have propulsion systems that allow them to remain submerged for longer periods of time than the three nuclear-capable submarines already in Israel's fleet, the Jerusalem Post reported.

The latest submarines not only would be able to carry out a first strike should Israel choose to do so, but they also would provide Israel with crucial second-strike capabilities, said Paul Beaver, a London-based independent defense analyst.

Israel is already believed to have that ability in the form of the Jericho-1 and Jericho-2 nuclear-capable ballistic missiles, which are buried so far underground they would survive a nuclear strike, he said.

"The Iranians would be very foolish if they attacked Israel," Beaver said.

German officials have said the contract for the new submarines was signed on July 6, and the Jerusalem Post reported this week the subs will be operational shortly.

Israel, operating on a policy of nuclear ambiguity, has never confirmed or denied whether it has nuclear weapons. It is believed, however, to have the world's sixth-largest stockpile of nuclear weapons, including hundreds of warheads.

Iran so far has resisted calls by the U.N. Security Council to halt uranium enrichment, despite an Aug. 31 deadline that is accompanied by the threat of sanctions.

The dispute over Tehran's nuclear program revolves around Iran's insistence that it wants to master the technology simply to generate electricity. Critics say Iran wants to make nuclear weapons.

The Dolphin submarine could be one of the best deterrents, Beaver said. The technology on the submarines makes them undetectable and gives them defensive capabilities in the case of attack, he said.

"They are very well-built, very well-prepared, lots of interesting equipment, one of the best conventional submarines available," Beaver said. "We are talking about a third string of deterrence capabilities."

Michael Karpin, an expert on Israel's nuclear capabilities who published a book on the issue in the United States, said nuclear submarines provide better second-strike capabilities than missiles launched from airplanes.

"Planes are vulnerable, unlike nuclear submarines that can operate for an almost unlimited amount of time without being struck," Karpin said. "Second-strike capabilities are a crucial element in any nuclear conflict."

In Germany, members of two opposition parties criticized the deal. Winfried Nachtwei, national security spokesman for the Greens, said the decision was wrong because Germany had obtained no guarantee the submarines would not be used to carry nuclear weapons.

"This red line should not be crossed," Nachtwei was quoted as saying by the taz newspaper. "Otherwise it is a complete renunciation of Germany's policy of non-proliferation."

David Menashri, an Israeli expert on Iran, said Tehran is clearly determined to obtain nuclear power and "the purchase of additional Dolphin submarines by Israel is a small footnote in this context."

What also makes Tehran dangerous, Beaver said, is that it may not understand the consequences of carrying out a nuclear strike.

"They (Iran) have a belligerent leadership and that's why Israel is prudent in ensuring that it has that deterrent capability," Beaver said. "What they (the submarines) are is a very good insurance policy."